1. Field of the Invention
The present invention relates generally to semiconductor devices and methods of manufacturing the same, and more particularly to a semiconductor device including carbon nanotubes in an interconnection layer and through electrodes and a method of manufacturing such a semiconductor device.
2. Description of the Related Art
Application of carbon nanotubes to the interconnects of a large scale integrated circuit (LSI) is taken as an example of their application to electronics. Carbon nanotubes range from a few to tens of nm in diameter, and are as long as a few nanometers in length. Because of its one-dimensional electronic properties due to this shape anisotropy, the carbon nanotube characteristically has a maximum current density allowing the flowing of current without disconnection of 1,000,000 A per square centimeter, which is 100 times or more as high as that of a copper interconnect. Further, with respect to heat conduction, the carbon nanotube is ten times as high in conductivity as copper. In terms of electric resistance, it has been reported that transportation without scattering due to impurities or lattice vibration (phonon), or so-called “ballistic electron transportation,” can be realized with respect to electrons flowing through the carbon nanotube. It is known that resistance per carbon nanotube in this case is approximately 6.45 kΩ. The carbon nanotube ranges widely from 0.4 to 100 nm in diameter, and its diameter is formed in a self-organizing manner. Therefore, the carbon nanotube is characterized by an extremely limited fluctuation along its length. Because of these characteristics, a highly reliable, extremely fine metal interconnect with less migration, which is a failure mode due to high current densities, is expected to be realized in the case of applying the carbon nanotube to an LSI interconnect.
Well-known methods of growing a carbon nanotube include arc discharge, laser ablation (laser vaporization), chemical vapor deposition (CVD), and SiC sublimation. According to these methods, transition metal is known to be employed as catalyst metal in forming a carbon nanotube. According to CVD and SiC sublimation, a catalyst metal layer is formed, and patterning is performed on the catalyst metal layer using lithography or etching employed in semiconductor LSI. Thereby, the position of growth of the carbon nanotube can be controlled.
The carbon nanotube is known to grow with a catalyst metal being fixed to its root or tip. The former case is referred to as a so-called root-growth mode, and the latter case is referred to as a tip-growth mode.
In the case of selectively forming carbon nanotubes, a process of patterning a catalyst metal layer is additionally required, which is a disadvantage in terms of the production cost and the reliability of a semiconductor device. The remaining of catalyst metal such as Fe or Co may be a problem in some semiconductor devices.
Accordingly, Japanese Laid-Open Patent Applications No. 2001-32071 and No. 2002-115070 propose generation methods according to which a metal layer of Ti or Ni or a layer of a nitride of such metal is provided under a catalyst metal layer, and carbon nanotubes are grown on the catalyst metal layer in a region where the metal layer or the metal nitride layer is formed.
However, according to such methods, the growth mode of the carbon nanotube cannot be controlled sufficiently. This results in a problem in that the above-described electric characteristics of the carbon nanotube cannot be fully realized in the case of employing carbon nanotubes as interconnect material in the interconnection part and the vertical interconnection part of a semiconductor device. Further, if complete removal of catalyst metal is required, there is a problem in that the catalyst layer remains at the root of any carbon nanotube grown in a root-growth mode, thus resulting in insufficient removal of the catalyst metal.
Further, in the case of employing the carbon nanotube in a vertical interconnection part, such as a via, of a semiconductor device, the catalyst metal layer and Al or Cu used in an interconnection part connected to the vertical interconnection part are subject to interdiffusion, thus resulting in the problem of a decline in the catalytic function. Further, when an interlayer insulating film is formed on the catalyst metal layer, a plasma or ions collide or come into contact with the surface of the catalyst metal layer, thus causing physical damage thereto. This also results in the problem of a decline in the catalytic function.